Lighting equipment for illumination and displays for image output have fundamentally different requirements, for example, for consumer applications.
Electrically powered artificial illumination lighting has become ubiquitous in modern society. Electrical lighting equipment is commonly deployed, for example, in homes, buildings of commercial and other enterprise establishments, as well as in various outdoor settings.
In conventional luminaires, the luminance output can be turned ON/OFF and often can be adjusted up or dimmed down. In some devices, e.g., using multiple colors of light emitting diode (LED) type sources, the user may be able to adjust a combined color output of the resulting illumination. The changes in intensity or color characteristic of the illumination may be responsive to manual user inputs or responsive to various sensed conditions in or about the illuminated space.
The optical distribution of the light output in the luminaire, however, typically is fixed. Various different types of optical elements are used in such lighting devices to provide different light output distributions, but each type of device has a specific type of optic designed to create a particular light distribution for the intended application of the lighting device. The dimming and/or color control features do not affect the distribution pattern of the light emitted from the luminaire.
There also have been proposals to use displays or display-like devices mounted in or on the ceiling to provide variable lighting. The Fraunhofer Institute, for example, has demonstrated lighting equipment using luminous tiles, each having a matrix of red (R) LEDs, green (G), blue (B) LEDs and white (W) LEDs as well as a diffuser film to process light from the various LEDs. The LEDs of the system were driven to simulate or mimic the effects of clouds moving across the sky. Although use of displays allows for variations in appearance that some may find pleasing, the displays or display-like devices typically have been optimized for image output and do not provide particularly good illumination for general lighting applications. A display typically has a Lambertian output distribution over substantially the entire surface area of the display screen, which does not provide the white light intensity and coverage area at a floor or ceiling height offered by a similarly sized ceiling-mounted light fixture.
Liquid crystal displays (LCD) also are rather inefficient. For example, backlights in LCD televisions have to produce almost ten times the amount of light that is actually delivered at the viewing surface. Therefore, any LCD displays that might be used as lighting products need to be more efficient than typical LCD displays for the lighting device implementation to be commercially viable.
Projection displays are typically cost effective alternatives to direct-view displays such as LCDs, when large area and high brightness are desired. But the color quality and light distribution from prior projection displays are not sufficient for general lighting applications.
Examples of other uses of lighting in combination with display technologies include various configurations of signage that include light sources as backlighting that are positioned behind a design feature such a diffuser or screen with an image or wording. Examples of such backlit signage includes advertising signs, door exit signs and other examples of signage that would benefit from backlighting. Some of the signs may be controllable to change wording or an image presented on the display device of the sign. In some instances of advertising signage, a transparent display can be used to provide advertising without obstructing a view of either the interior of a store when viewed from the exterior or vice versa, as well as providing an easily changeable design. However, backlit signage without additional lighting is not typically configured to provide general illumination that complies with governmental regulations and industry standards applicable to the environment in which the signage is installed.